1. Field of the Invention
This invention relates to a magnetic recording medium evaluation apparatus and a magnetic recording medium evaluation method, and more specifically, relates to a magnetic recording medium evaluation apparatus for a hard disk magnetic recording medium, and to an evaluation method for such a medium.
2. Description of the Related Art
In magnetic recording and reproduction systems used in hard disk devices, PRML (partial response maximum-likelihood) technology is employed to perform high-density recording and reproduction. On the other hand, in the evaluation of magnetic heads and magnetic recording media used to construct magnetic recording and reproduction systems, recording is normally performed at fixed magnetization inversion intervals by causing inversion of the recording magnetic field of the magnetic recording head at equal time intervals in the magnetic recording medium rotating at constant velocity, and performing frequency-axis analyses of electrical signals obtained by a magnetoresistive reproduction element, again during rotation at constant velocity, to evaluate analog signal quality. In particular, the signal-to-noise ratio evaluated by a spectrum analyzer (MF-SpiSNR) when signals are recorded and reproduced at twice the interval of the specified magnetization inversion interval is widely used for evaluations of the signal quality of a magnetic recording and reproduction system, or of a magnetic recording medium, when the error rate is not directly measured. However, there are cases in which a highly customized dedicated LSI is used to perform random-pattern recording and reproduction in a specified channel, to evaluate the error rate directly.
While the above-described MF-SpiSNR is closely correlated with the error rate in relative evaluations of magnetic recording media when the macroscopic structure is substantially the same and processes are different, when performing evaluations of magnetic recording media with different structures, there is a problem that good correlation cannot necessarily be obtained. In order to measure directly the error rates for magnetic recording media with different structures, a dedicated signal processing circuit is required in addition to an analog signal evaluation system, and so there is a problem that such a magnetic recording medium evaluation apparatus is of limited applicability.